Evaporative cooling system employing liquid film evaporation from grooved evaporator surface and vapor push pump for circulating liquid

ABSTRACT

Within a vaporization chamber which houses apparatus to be cooled (e.g., a transformer) a film of liquid flowing over a heated surface of said apparatus is evaporated thereby cooling the apparatus. The surface includes grooves which stabilize the distribution of a flowing liquid film so that all sections of the surface are maintained in a wetted condition by the flowing film thereby eliminating, or significantly reducing, the occurrence of dry, and therefore hot, spots on the surface. A vapor push pump within the vaporization chamber recirculates liquid so that the liquid can be redistributed as a flowing film over the aforesaid grooved surfaces. The use of a vapor push pump in combination with grooved evaporator surfaces, inter alia, enables significant efficiencies and economies respecting, among other things, the circulation rate of liquid coolant required.

United States Patent- 1191 Staub et al.

[ June 3,1975

[75] Inventors: Fred W. Staub; Philip G. Kosky,

both of Scotia, N.Y.

[73] Assignee: General Electric Company,

Schenectady, NY.

22 Filed: Mar. 20, 1974 21 Appl.No.:452,945

Related US. Application Data [63] Continuation of Ser. No. 310,323, Nov.29, 1972,

abandoned.

[52] US. Cl 174/15 R; 165/105 [51] Int. Cl. H01f 27/18 [58] Field ofSearch. 174/15 R, 15 C, 16 R, 16 DH; 165/105; 417/134, 135, 136,138,208, 209; 336/55, 57, 58, 61

[56] References Cited UNITED STATES PATENTS 1,708,600 4/1929 Beckman174/15 R 2,924,635 2/1960 Narbut 174/15 R 3,261,905 7/1966 Allen 417/209X 3,402,767 9/1968 Bohdansky et a1. 165/105 3,452,147 6/1969 Narbut eta1. 174/16 R Primary ExaminerArthur T. Grimley Attorney, Agent, orFirm-Paul R. Webb, 11; Joseph T. Cohen; Jerome C. Squillaro [5 7]ABSTRACT Within a vaporization chamber which houses apparatus to becooled (e.g., a transformer) a film of liquid flowing over a heatedsurface of said apparatus is evaporated thereby cooling the apparatus.The surface includes grooves which stabilize the distribution of aflowing liquid film so that all sections of the surface are maintainedin a wetted condition by the flowing film thereby eliminating, orsignificantly reducing, the occurrence of dry, and therefore hot, spotson the surface. A vapor push pump within the vaporization chamberrecirculates liquid so that the liquid can be redistributed as a flowingfilm over the aforesaid grooved surfaces. The use of a vapor push pumpin combination with grooved evaporator surfaces, inter alia, enablessignificant efficiencies and economies respecting, among other things,the circulation rate of liquid coolant required.

3 Claims, 4 Drawing Figures PATEHTEMuz-a [975 4 7 SHEET EVAPORATIVECOOLING SYSTEM EMPLOYING LIQUID FILM EVAPORATION FROM GROOVED EVAPORATORSURFACE AND VAPOR PUSH PUMP FOR CIRCULATING LIQUID This is acontinuation of application Ser. No. 310,323, filed Nov. 29, 1972, nowabandoned.

CROSS-REFERENCES TO RELATED APPLICATIONS Hereinafter disclosed, but notclaimed herein, is a vapor push pump which may, advantageously, beemployed as the liquid recirculation pump in the combination forming theliquid film evaporative cooling system of the subject invention; saidvapor push pump being both disclosed and claimed in the U.S. patentapplication, Ser. No. 310,662, filed Nov. 29, 1972, on even dateherewith, now U.S. Pat. No. 3,819,301 in behalf of the inventors H..Iaster and P. G. Kosky, titled SIN- GLE VALVE VAPOR PUSH PUMP.

A related novel vapor push pump is also disclosed in the U.S. patentapplication Ser. No. 310,437, filed Nov. 29, 1972, on even dateherewith, now U.S. Pat. No. 3,834,835 in behalf of the inventors H.Jaster, P. G. Kosky and F. W. Staub, titled DOUBLE VALVE VAPOR PUSHPUMP.

Also, an example of a liquid film evaporative cooling system, with whichthe subject invention is concerned, as well as some sophisticationswhich may be included therein is to be had by referring to theearlier-filed U.S. patent application, Ser. No. 266,065, filed June 26,1972, now abandoned in behalf of F. W. Staub titled VAPORIZATION COOLINGSYSTEM USING A SEGREGATED NON-CONDENSIBLE DIELECTRIC GAS FORPRESSURIZING A VAPOR COOLANT AND MAINTAINING DIELECTRIC STRENGTH WITHOUTSIGNIFICANTLY INTERFERING WITH CONDENSATION OF THE VAPOR.

The entire right, title and interest in and to the inventions describedin the aforementioned patent applications, as well as in and to theaforementioned patent applications, and the entire right, title andinterest in and to the invention herein disclosed, as well as in and tothe patent application of which this specification is a part, areassigned to the same assignee.

BACKGROUND OF THE INVENTION 1. Field of the Invention The subjectinvention pertains, in general, to the cooling of apparatus (e.g.,transformers, etc.) by evaporating a film of liquid from the surface, orsurfaces, of the apparatus; and, in particular, to a film evaporationcooling system including, inter alia, liquid pumping means forsupplementing condensate coolant, film flow over said surfaces, saidsurfaces including grooves therein for stabilizing the distribution ofthe flowing film of liquid coolant.

Although the subject invention is hereinafter described, and illustratedin the accompanying drawing figure, in connection with the liquid filmevaporation cooling of static heat producing electrical apparatus, suchas a transformer, it is to be understood that the invention may beotherwise employed. For example, the heat producing apparatus need notbe electrical and, if electrical, it need not be static. However, forpurposes of illustration the subject invention is hereinafter disclosedas being incorporated in the hereinbefore identi- .fied vaporizationcooling system disclosed in U.S. pa-

tent application Ser. No. 266,065, filed June 26, 1972, in behalf of F.W. Staub.

2. Description of Prior Art Closed, or hermetically sealed, filmevaporation cooling systems employing two-phase fluid coolants have beenproposed. In such systems the fluid coolant is distributed while in itsliquid phase as a liquid film over a surface, or surfaces, of theapparatus to be coded. Heat transfer from the heated surface of theapparatus to the liquid film evaporates the film thereby cooling thesurface and the apparatus. Where the apparatus to be cooled iselectrical in nature (e.g., a transformer, etc.) the two-phase fluidcoolant is a dielectric and, sometimes, an inert non-condensibledielectric gas is used in addition to the aforesaid two-phase fluid; theinert non-condensible gas serving to maintain adequate system pressureand dielectric strength. In the aforementioned film evaporation coolingsystem the vapor produced subsequently condenses and is redistributed asa liquid film over the surfaces of the apparatus to be cooled. Theevaporation-condensation cycle causes a natural recirculation of thecoolant. However, it has been found that the flowing liquid coolantcannot normally be maintained intact on smooth surfaces unlesssubstantial liquid coolant is caused to fiow in addition to theaforementioned natural recirculation rate. If the aforesaid rupture ofthe liquid film occurs then large dry and therefore hot spots are formedon the surfaces to be cooled resulting in undesirably high temperatures.To reduce the said undesirable situation either excess liquid may bepumped to the cooling surfaces in addition to the condensate flow, orthe apparatus to be cooled may be partially submerged in a pool of theliquid coolant.

SUMMARY OF THE INVENTION One object of the invention is to provide acooling system wherein apparatus to be cooled by evaporation of a filmof liquid coolant therefrom need not have substantial portions of theapparatus immersed in a pool, or reservoir, of the liquid coolant.

Another object of the invention is to provide a film evaporation coolingsystem wherein the quantity of the two-phase fluid coolant required is,under the circumstances, the minimum quantity.

Another object of the invention is to provide a film evaporation coolingsystem which can satisfactorily perform the required cooling ofapparatus throughout a wide range embracing a relatively low heat fluxcondition of the apparatus to a design heat flux condition of theapparatus.

Another object of the invention is to provide a film evaporation coolingsystem wherein liquid film is maintained intact to insure intact liquidfilm flow in order to at least reduce to a minimum the formation of hot,or dry, spots on the surfaces of the apparatus to be cooled.

In accordance with the invention there is provided a film vaporizationcooling system comprising: a vaporization chamber containing heatproducing apparatus to be cooled and a two-phase fluid coolantcomprising a liquid and a vapor, said liquid residing at a bottomportion of the chamber and having a liquid level above the bottom of thechamber, said liquid also being distributed as a film which coats saidapparatus, said vapor being produced by vaporization of said liquid bythe heat produced by said apparatus, said vapor occupying space in saidchamber above said liquid level; a condenser coupled with saidvaporization chamber for receiving vapor from said vaporization chamber,condensing the received vapor and enabling its return as a liquid tosaid chamber; means in said vaporization chamber for receiving theliquid from said condenser and enabling the distribution of said liquidas a film coating said apparatus; and, a vapor push pump for pumpingliquid from said liquid residing at the bottom portion of said chamberto said means for enabling the distribution of liquid as a film.

An additional feature of the invention is the inclusion of a number ofgrooves in the surfaces of the heat pro ducing apparatus to be cooled.The grooves enable the liquid which is coating the apparatus to maintainan intact liquid film thereon thereby significantly reducing theoccurrence of hot or dry spots on said surfaces for a minimum liquidcoolant rate.

Other objects and features, as well as the many advantages of theinvention, appear hereinafter whereat the invention is disclosed bymeans of an illustrative example with reference to accompanying drawingfigures.

THE DRAWINGS FIG. 1 is a schematic diagram of the film vaporizationcooling apparatus according to the invention showing a vaporizationchamber, a condenser, and an inert gasholding reservoir, a transformerto be cooled within the vaporization chamber and'a vapor push pump.

FIG. 2 is a cross section view taken on section line 2-2 of FIG. 1.

FIG. 3 is another cross section view taken on section line 33 of FIG. 2.

FIG. 4 is a schematic diagram of one form of vapor push pump which maybe employed in the combination shown in FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENT In the schematic diagram shown inFIG. 1 a transformer designated, generally, by the reference number 11includes a core 13 of laminated magnetic steel on which a number ofconductor windings embedded in a matrix 15 of insulating material aredisposed. The transformer 11 may be mounted on a suitable pedestal (notshown) of dielectric material. As shown the transformer 11 is locatedwithin a vaporization chamber 17 of a transformer casing 19. A surfacecondenser 23 is coupled in series between chamber 17 of casing 19 and agas-holding reservoir 25. The system including the vaporization chamber17, the condenser 23 and gasholding reservoir 25 form a closed, orhermetically sealed, system. The system is charged with a mass ofvaporizable dielectric liquid, such as an inert fluorocarbon liquid;e.g., perfluoro-2-butyltetrahydrofuran which is marketed under thedesignation FC-75 of the 3M Company. The system is also charged with aninert non-condensible dielectric gas such as sulfur hexafluoride (SP Thefluorocarbon liquid coolant has a high dielectric strength. Howeover,the dielectric strength of its vapor varies directly with its density.Accordingly, at low system temperatures when the vapor density is lowlittle dielectric protection is provided. Accordingly, thenon-condensible inert dielectric gas is charged into the system toregulate the system pressure for the purpose of maintaining thedielectric strength in the vapor phase in the chamber 17 when the systemtemperature is low. It is to be understood that the aforementioned inertfluorocarbon liquid coolant and inert gas are specifically named hereinas examples and that other liquid coolants and inert non-condensiblegases may be employed. The operation of a film vaporization coolingsystem employing the combination of a non-condensible dielectric gas anda dielectric two phase fluid coolant is disclosed in the U.S. patentapplication Ser. No. 266,065 of F. W. Staub, hereinbefore more fullyidentified.

In FIG. 1 the condenser 23 is illustrated as an aircooled surfacecondenser comprising a plurality of condenser tubes, such as the tubes27 and 29. Each of the tubes 27 and 29 may be provided with spacedcooling fins 31 31 which are connected to the outer wall surfaces of thetubes and, as is well known, such cooling fins promote heat transferfrom the tubes. The tube 27 is open at both ends, 27a and 2717; theopening 27a serves as a vapor inlet as well as a condensate outlet port.As indicated the tube opening 27a is coupled to and communicates withthe top of the vaporization chamber 17. The tube opening 27b is coupledto and communicates with the gas-holding reservoir 25. Similarly, thecondenser tube 29 is open at both ends, 29a and 29b. The opening 29aserves as both a vapor inlet and condensate outlet port and is coupledto and communicates with the top of the vaporization chamber 17. Thetube opening 2% is coupled to and communicates with the gas reservoir25. Mounted within the vaporization chamber 17 near the top thereof andsituated di rectly below the tube openings 27a and 29a is a perforateddrip pan 33 which is arranged to receive condensate exiting from theopenings 27a and 29a of the surface condenser 23. Being perforated thepan 33 enables condensate collected therein to be distributed over thesurfaces of the transformer 11. The liquid collected in the pan 33 dripsor falls on the core 13 which may contain one or more cooling ducts andon insulating matrix 15 where is formed a liquid film which coats thesurfaces of the transformer 11. FIGS. 2 and 3, hereinafter discussed,illustrate grooved surfaces. The excess liquid collects in a pool 18 orbody of liquid in the bottom of vaporization chamber 17. The pool 18 ofliquid coolant, having the liquid level II measured from the bottom ofthe chamber 17 of casing 19 includes the bottom portion of the core 13immersed therein.

In FIG. 1 two condenser tubes 27 and 29 of surface condenser 23 havebeen shown diagrammatically. However, it is to be understood that morethan, or less than, two condenser tubes may be employed for connectingthe vaporization chamber 17 with the gas holding reservoir 25, dependingon the heat transfer rate required for the specific purpose.

At, for example, median ambient design temperatures the vaporizabledielectric liquid coolant pool 18 fills the bottom portion ofvaporization chamber 17 of casing 19 to the level H, as indicated. Heatproduced by the transformer 11 vaporizes the liquid film thereby coolingthe transformer. The vapor moves upwardly in the vaporization chamber 17and enters the condenser 23 through the inlet openings 27a and 29a. Thenoncondensible dielectric gas is normally largely confined in thereservoir 25 if its vapor density is less than that of the dielectricvapor. The dielectric gas in effect, closes off the opposite ends 27band 29b of the condenser tubes 27 and 29. With the ends 27b and 29bclosed by the gas, the vapor moves upwardly in the tubes 27 and 29 andcondenses on the inner wall surfaces of these tubes. The condensate,thus formed, on

the inner wall surfaces of the tubes 27 and 29 flows downwardly andultimately exits as a liquid condensate from the openings 27a and 29aand collects in the perforated drop pan 33. From the pan 33 thecondensate is distributed over the surfaces of the transformer 11. Thus,the condensate formed in the condenser tubes returns by gravity, incountercurrent flow relationship with the vapor in the tubes, to the pan33 where, again, by means of gravity it is distributed within the core13 and matrix as a film. Subsequently, the heat producing transformer 11again vaporizes the liquid film thereby rejecting its heat. Thisvaporizationcondensation cycle is repeated and the temperature of thetransformer 11 is maintained within safe operating limits.

Also located within the vaporization chamber 17 is a vapor push pump 10for recirculating condensate from the pool 18 or body of liquid back tothe drip pan 33. The inclusion of a vapor push pump such as the vaporpush pump 10 is advantageous. Without a pump 10 to recirculate thecondensate from the pool 18 to the drip pan 33 the only liquid return isby the process of the vaporization and subsequent condensation cycle. Insuch a situation a large mass of the apparatus to be cooled (e.g.,transformer 11) must then be immersed in the liquid 18. The details ofthe vapor push pump 10 are illustrated to the schematic cross sectiondrawing of FIG. 4. As indicated, the pump 10 includes a housing 12within which there is defined a chamber 14. Housing 12 has a port 16 atthe top thereof so that liquid from the external body 18 or pool ofliquid may enter port 16 and at least partly fill the chamber 14. Thehousing 12 is adapted to be submerged in the external body of coolantliquid 18 whose head H, is shown in FIGS. 1 and 4 as being the distancefrom the liquid level of the body of liquid 18 to the top of the housing12. Also, at the top of the housing 12 two additional openings 20 and 22are provided. The opening 20 has one end of a conduit 24 coupledthereto. The conduit 24 has another opening 21 at an opposite endthereof. The opening 21 is above the level of the body of liquid 18. Theopening 20 with conduit 24 serves as a vapor vent, the action of whichis hereinafter described. Another conduit 26 which is relatively longpasses through the opening 22 in the housing 12. The conduit 26 issealed to the housing 12 where it passes through opening 22. Asindicated conduit 26 has an inlet opening 28 at the lower end thereofand an outlet opening 30 at the upper end thereof. The conduit 26 actsas a liquid delivery tube in that the liquid within housing 12 (inchamber 14) is pushed through inlet opening 28 and flows upwardly inconduit 26 where it is discharged at the outlet opening 30 and into thedrip pan 33 (of FIG.

- 1) in vaporization chamber 17 (of FIG. 1). The outlet opening 30 isabove the external body 18 of liquid. Inlet opening 28 is submerged inliquid in chamber 14 in housing 12. Situated in chamber 14 is a body 32of low thermal conductivity and low thermal diffusivity. The body 32includes a bore 34 within which an electric cartridge type heater 36 islocated. A pair of electrical leads 38 having an end thereofelectrically connected with the heater 36 extends in sealed relationshipthrough the housing 12 to the outside thereof. If desired, the leads 38may also extend through the transformer casing 19 so that electricalenergization of the heater 36 may be initiated entirely from without the.transformer housing 19. The upper portion of the bore 34 communicateswith a wider diameter cylindrical space 40 which is closed at its upperend by a seal 60,

or cover. Body 32 also includes a cylindrical well 42 within which theinlet opening 28 of conduit 26 is positioned. Between an outside wallsurface of the body 32 and the inside wall surface of housing 12 thereis provided the space 44 as shown. Body 32 also includes another bore 46which communicates the aforesaid space 44 with the other bore 34 withinwhich heater 36 is positioned.

Mounted by suitable means (not shown) at the upper portion of thecylindrical space 40 is a bent vapor outlet tube 48, an inlet end 50 ofwhich is within the cylindrical space 40 and an outlet end 52 of whichextends above the uppermost part of the sealing cover 60.

Mounted within chamber 14 is a valve body 54. Valve body 54 is buoyantand may float upwardly or downwardly depending on the liquid level inchamber 14. The upward and downward movement of the valve body 54 isindicated by the arrows in the drawing. Valve body 54 includes a numberof openings 58 therein to allow for the passage of vapor therethrough.

Suitable stop members (not shown) limit the downward, as well as lateralmovement of valve body 54. In its uppermost position the valve body 54seals and closes off the port 16 and opening 20. Valve body 54 includesa flexible diaphragm 56 at the top thereof which facilitates closure ofport 16 and opening 20. The diaphragm 56 flexes and thereby enters ashort distance into the port 16 and into opening 20 for closing theseapertures. One suitable material, among others, for fabricating thediaphragm 56 is a thin sheeting of silicone rubber.

Heat generated by heater 36 efficiently raises the temperature of theliquid surrounding the heater and is not wastefully employed in heatingbody 32 which is fashioned of thermal insulation material. Moreover,heat is not wastefully employed in heating the housing 12 or the body ofliquid 61, inter alia.

Operationally, the valve body 54 due to its own weight is situated moreor less in the position shown in FIG. 4 and is retained by stop members.In such a position the port 16 and the opening 20 are open. As a resultliquid from body 18 enters port 16. The liquid thus admitted fills thechamber 14. When the liquid level in chamber 14 reaches the valve body54 the buoyancy of the valve body 54 causes it to float upwardly in theliquid thereby closing the port 16 and the opening 20. Some of theliquid within chamber 14 enters space 44 and thereafter enters bore 46from whence it passes to the other bore 34 to surround heater 36. Heater36 adds heat to the surrounding liquid and converts it to vapor whichrises into the space 40. Vapor from space 40 enters inlet opening 50 andpasses therethrough to the outlet opening 52. From outlet opening 52 thevapor exits through openings 58 in valve body 54. Vapor exiting fromopenings 58 enters the main chamber 14 where it accumulates and exertspressure on the liquid 61 therebelow. The vapor contained in the upperportion of chamber 14 also acts on the underside of diaphragm 56 to helpmaintain diaphragm 56 in a position closing port 16 and opening 20.Also, vapor in the upper portion of chamber 14 exerts pressure on theliquid in the lower portion of the chamber 14 thereby pushing or forcingthe liquid into riser conduit 26 and through the inlet opening 28thereof. The liquid entering the inlet opening 28 passes outwardlythrough con- 7 duit 26 and is discharged at opening 30 into the drip pan33. (See FIG. 1) When the liquid level within chamber 14 has fallen to alevel a little below the lower periphery or rim of the conduit 26 withinthe well 42 the conduit 26 drains free of liquid and the vapor withinchamber 14 and within conduit 26 is in effect vented through conduit 26and discharged at outlet opening 30. Accordingly, the vapor pressurewithin the chamber 14 is relieved and the valve body 54 falls due to itsown weight, thus opening the port 16 and the opening '20. Also includedin combination with vapor push pump 10 is a vapor venting conduit 24. Ifsuch a conduit 24 were not provided then float valve body 54 when moveddownwardly to open inlet port 16 would not permit vapor in chamber 14 toescape other than through the port 16 during the time that liquid frombody 18 was also being admitted through the same port 16. Byincorporating a vapor venting conduit 24 with its opening 20 the vaporfinds a low impedance path through opening 20 in conduit 24 to escapefrom pump The vapor push pump 10 will operate even though dielectric gasis occluded in the liquid coolant 18 and is later on enabled to escape.

Another feature of the invention is illustrated in FIGS. 2 and 3 wheredifferent sectional views of the insulation matrix are shown. As shownin FIG. 2 the matrix 15 has a plurality of longitudinal ducts 35extending therethrough vertically. The ducts 35 serve as cooling ducts.The liquid from the drip pan 33 falls onto the matrix 15 and enters thecooling ducts 35, forming therein on the side wall surfaces thereofliquid films which flow downwardly within the ducts 35 to the body ofliquid 18. Although a specific number of cooling ducts 35 are indicatedin FIG. 2 it is to be understood that more than or less than thespecifically illustrated number of ducts 35 may be employed, dependingon the maximum temperatures allowed. In the vertical cross section viewshown in FIG. 3 a section of one such duct 35 is clearly illustrated. Asindicated, the duct 35 has a plurality of grooves 37 formed, orotherwise provided, in its side wall. The longitudinally extendingvertical grooves 37 serve to maintain the film of liquid intact so thatfilm will not break into rivulets (as would be the case with a smoothsurface) thereby preventing rupture of the film. The aforesaid ruptureby the coolant film would allow dry and therefore hot spots to exist.

Although one more or' less specific embodiment of the invention has beendescribed and illustrated in the accompanying drawings, it is to beunderstood that this has been done for purposes of providing a workingexample of the invention and that many changes, not departing from theinventive principles involved, will occur to those skilled in the art.The scope of the invention is to be determined from the claimshereinafter set forth. V

What is claimed is:

1. In combination: a vaporization chamber containing heat producingelectrical apparatus to be cooled while dielectrically protected and atwo phase dielectric fluid comprising a liquid and a vapor, saidapparatus including at least one cooling duct extending verticallytherethrough, said duct having a plurality of longitudinal extendingvertical grooves in its side wall, said liquid residing at a bottomportion of the chamber and having a liquid level above the bottom of thechamber,

said liquid also being distributed as a film which coats said apparatusand coats the vertical grooves of said duct, said vapor being producedby vaporization of said liquid by said heat produced by said apparatus,said vapor occupying space in said chamber above said liquid level, acondenser having one end thereof connected to and communicating with anupper portion of said vaporization chamber occupied by said vapor, areservoir containing a predetermined mass of noncondensable dielectricgas positioned above said condenser, said condenser having another endconnected to and communicating with said reservoir and said gas therein,said gas forming an interfacial contact with said vapor in saidcondenser at a region therein between said ends of said condenser, saidvapor condensing to form liquid condensate in the condenser on one sideof said interfacial contact so that the effective condensation area ofsaid condenser lies between said one end of said condenser and saidinterfacial contact; distribution means in said chamber positioned abovesaid electrical apparatus for receiving liquid condensate from saidcondenser and distributing the liquid condensate as a film coating saidapparatus and coating the vertical grooves of said duct, and acondensate makeup pump for pumping liquid from the bottom portion of thechamber to said distribution means.

2. A hermetically sealed system comprising a chamber including heatproducing electrical apparatus therein, said apparatus having at leastone surface which includes a plurality of grooves therein, said at leastone surface and said plurality of grooves therein being inclined towarda vertical axis of said apparatus, a reservoir located above saidchamber, a condenser connected between said chamber and said reservoirand establishing communicationtherebetween, a two phase fluid coolantcomprising a dielectric liquid and its dielectric vapor confined in saidsystem, a noncondensible dielectric gas, said gas being largely combinedin said reservoir and making contact with said vapor in said condenser,said vapor being largely confined within said chamber and extending intosaid condenser to the region of contact with said gas, said vaporcondensing to form liquid condensate, distribution means for receivingsaid liquid condensate from said condenser and distributing the liquidcondensate as a film coating the grooves of said at least one internalsurface and coating said apparatus, and a condensate make-up pump insaid chamber for pumping liquid therein between a lower portion of saidapparatus to said distribution means.

3. In combination: a vaporization chamber having upper and lowerportions, heat-producing apparatus within said chamber, said apparatushaving at least one surface which includes a plurality of groovestherein, said at least one surface and said plurality of grooves thereinbeing inclined toward a vertical axis of said apparatus, a two-phasefluid coolant within said chamber, said fluid coolant having a liquidphase and a vapor phase, part of the liquid phase coolant residing atthe lower portion of said chamber, the vapor phase coolant beingproduced by vaporization of the liquid phase coolant by said apparatus,a condenser coupled with the top portion of said chamber for receivingvapor phase coolant therefrom and returning liquid phase coolantthereto, means within said chamber at the top portion thereof forreceiving liquid phase coolant from the condenser and distributing saidcoolant as a liquid 3,887,759 9 l film on said at least one surface andin the grooves for transporting liquid phase coolant from the lowertherein so that the liquid film stays intact, without forming rivulets,as the liquid film migrates downwardly in said grooves for collection atthe lower porher at the top porno thereof tion of said chamber, and acondensate make-up pump portion of the chamber to said means within thecham-

1. In combination: a vaporization chamber containing heat producing electrical apparatus to be cooled while dielectrically protected and a two phase dielectric fluid comprising a liquid and a vapor, said apparatus including at least one cooling duct extending vertically therethrough, said duct having a plurality of longitudinal extending vertical grooves in its side wall, said liquid residing at a bottom portion of the chamber and having a liquid level above the bottom of the chamber, said liquid also being distributed as a film which coats said apparatus and coats the vertical grooves of said duct, said vapor being produced by vaporization of said liquid by said heat produced by said apparatus, said vapor occupying space in said chamber above said liquid level, a condenser having one end thereof connected to and communicating with an upper portion of said vaporization chamber occupied by said vapor, a reservoir containing a predetermined mass of non-condensable dielectric gas positioned above said condenser, said condenser having another end connected to and communicating with said reservoir and said gas therein, said gas forming an interfacial contact with said vapor in said condenser at a region therein between said ends of said condenser, said vapor condensing to form liquid condensate in the condenser on one side of said interfacial contact so that the effective condensation area of said condenser lies between said one end of said condenser and said interfacial contact; distribution means in said chamber positioned above said electrical apparatus for receiving liquid condensate from said condenser and distributing the liquid condensate as a film coating said apparatus and coating the vertical grooves of said duct, and a condensate makeup pump for pumping liquid from the bottom portion of the chamber to said distribution means.
 1. In combination: a vaporization chamber containing heat producing electrical apparatus to be cooled while dielectrically protected and a two phase dielectric fluid comprising a liquid and a vapor, said apparatus including at least one cooling duct extending vertically therethrough, said duct having a plurality of longitudinal extending vertical grooves in its side wall, said liquid residing at a bottom portion of the chamber and having a liquid level above the bottom of the chamber, said liquid also being distributed as a film which coats said apparatus and coats the vertical grooves of said duct, said vapor being produced by vaporization of said liquid by said heat produced by said apparatus, said vapor occupying space in said chamber above said liquid level, a condenser having one end thereof connected to and communicating with an upper portion of said vaporization chamber occupied by said vapor, a reservoir containing a predetermined mass of non-condensable dielectric gas positioned above said condenser, said condenser having another end connected to and communicating with said reservoir and said gas therein, said gas forming an interfacial contact with said vapor in said condenser at a region therein between said ends of said condenser, said vapor condensing to form liquid condensate in the condenser on one side of said interfacial contact so that the effective condensation area of said condenser lies between said one end of said condenser and said interfacial contact; distribution means in said chamber positioned above said electrical apparatus for receiving liquid condensate from said condenser and distributing the liquid condensate as a film coating said apparatus and coating the vertical grooves of said duct, and a condensate make-up pump for pumping liquid from the bottom portion of the chamber to said distribution means.
 2. A hermetically sealed system comprising a chamber including heat producing electrical apparatus therein, said apparatus having at least one surface which includes a plurality of grooves therein, said at least one surface and said plurality of grooves therein being inclined toward a vertical axis of said apparatus, a reservoir located above said chamber, a condenser connected between said chamber and said reservoir and establishing communication therebetween, a two phase fluid coolant comprising a dielectric liquid and its dielectric vapor confined in said system, a noncondensible dielectric gas, said gas being largely combined in said reservoir and making contact with said vapor in said condenser, said vapor being largely confined within said chamber and extending into said condenser to the region of contact with said gas, said vapor condensing to form liquid condensate, distribution Means for receiving said liquid condensate from said condenser and distributing the liquid condensate as a film coating the grooves of said at least one internal surface and coating said apparatus, and a condensate make-up pump in said chamber for pumping liquid therein between a lower portion of said apparatus to said distribution means. 